Circuit breakers provide overcurrent and short circuit protection for electric power systems. In the small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic trip device. Such a device includes a bimetal which is heated and bends in response to a persistent overcurrent condition thereby unlatching a spring powered operating mechanism which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system. An armature attracted by the sizable magnetic forces generated by a short circuit also unlatches, or trips, the operating mechanism.
In many applications, the miniature circuit breaker also provides ground fault protection. An electronic circuit detects leakage of current to ground and generates a ground fault trip signal. This signal energizes a shunt trip solenoid which unlatches the operating mechanism, typically through actuation of the thermal-magnetic trip device.
Recently, there has been considerable interest in also providing protection against arcing faults. Arcing faults are intermittent high impedance faults which can be caused for instance by worn insulation, loose connections, broken conductors, and the like. Because of their intermittent and high impedance nature, arcing faults do not generate currents of sufficient instantaneous magnitude or sufficient average current to rigger the thermal-magnetic trip device. Consequently, separate electrical circuits have been developed for responding to arcing faults.
Ground fault protection circuits and arc fault protection circuits typically include test circuits for affirming their continued operability. Currently, separate test switches, each with its own test button, are provided for performing the ground fault and arc fault tests. However, the molded cases of the miniature circuit breakers have been standardized for interchangeable use in load centers. There is limited space available in the standardized miniature circuit breakers for all of the additional circuitry required for ground fault and arc fault protection, let alone the test circuits.
U.S. patent application Ser. No. 09/069,355 filed on Apr. 29, 1998 discloses a miniature circuit breaker with a common rocker button which is rotated in one direction to actuate the ground fault test circuit, and the opposite direction to actuate the arc fault test circuit. The ground fault and arc fault test circuits are mounted on a common printed circuit board (PCB) and each has a spring contact arm projecting from the printed circuit board and which is deflected into contact with a common flexible contact extending between them by a separate finger on the common rocker button to actuate the associated test circuit. This arrangement works fine for circuit breakers where the circuit board is in close proximity to the common rocker button so that the spring contact arms can be directly engaged by the rocker button.
Unfortunately, on other miniature circuit breakers, the printed circuit board on which the test circuit is implemented is spaced from the test button so that the above-described direct engagement between a common rocker button and test switches is not possible.
There is a need, therefore, for improved miniature circuit breakers having both ground fault and arc fault test circuits.
More particularly, there is a need for such circuit breakers with a common test button which can separately actuate the ground fault and arc fault test circuits even though and the associated actuating switches are not in close proximity to the common test button.